The present invention relates to a discharge electrode, a high frequency plasma generator, a method of power feeding to a discharge electrode, and a method of manufacturing semiconductor device. More particularly, the present invention relates to a high frequency plasma generator used for forming a film of a semiconductor, such as amorphous silicon, microcrystal silicon, polycrystal thin silicon, silicon nitride and the like, used in a solar cell, a thin film transistor and the like, and etching a film of a semiconductor, and its discharge electrode, a method of power feeding to the discharge electrode, and a method of manufacturing semiconductor device using it.
As an example of a configuration of the high frequency plasma generator and a method of manufacturing semiconductor device using it, two typical examples of: {circle around (1)} a case of a usage of parallel plate electrodes; and {circle around (2)} a case of a usage of ladder electrodes are described in a case when amorphous silicon semiconductor thin film (hereafter, referred to as a-Si) is manufactured by using a plasma chemical vapor deposition apparatus (hereafter, referred to as a PCVD apparatus).
FIG. 11 shows one configuration example of an apparatus using the {circle around (1)} parallel plate electrodes usually used for the a-Si film formation. A substrate heater 2 is mounted within a reactor 1, and electrically grounded. A flat plate electrode 3 is mounted at a position opposite to the substrate heater 2, and it is placed, for example, 20 mm away from the substrate heater 2. An external high frequency power supply 4 is connected through an impedance matching device 5 and a coaxial cable 6 to the flat plate electrode 3. An earth shield 8 is mounted near the flat plate electrode 3 so that unnecessary plasma is not generated on a side opposite to a plane opposite to the substrate heater 2 of the flat plate electrode 3.
The a-Si film is formed in the following procedure.
At first, a substrate 16 on which the a-Si thin film is formed is placed on the substrate heater 2 whose temperature is set, for example, to 200xc2x0 C. SiH4 gas is introduced from a gas supply tube 17, for example, at a velocity of flow of 50 sccm. Then, a pressure within the reactor 1 is adjusted, for example, to 100 mTorr by adjusting an exhaust speed in a vacuum pump system (not shown) connected to a vacuum exhaust pipe 18.
The supply of high frequency electric power causes the plasma to be generated between the substrate 16 and the flat plate electrode 3. The impedance matching device 5 is adjusted such that the high frequency electric power is effectively fed to a plasma generator. The SiH4 is decomposed in a plasma 19. The a-Si film is formed on a surface of the substrate 16. The a-Si film having a necessary thickness is formed, for example, by carrying out the film formation under the above-mentioned condition for about ten minutes.
FIG. 12 shows one configuration example of the apparatus using the {circle around (2)} ladder electrode 303. The ladder electrode is reported in detail, for example, in Japanese Laid Open Patent Application (JP-A-Heisei, 4-236781).
FIG. 13 is a view illustrating the structure of the ladder electrode 303 drawn from an A-direction of FIG. 12 so that it can be sufficiently understood.
The substrate heater 2 (not shown in FIG. 13) is mounted within the reactor 1, and electrically grounded. The ladder electrode 303 is mounted at the position opposite to the substrate heater 2, and it is placed, for example, 20 mm away from the substrate heater 2. The external high frequency power supply 4 is connected through the impedance matching device 5 and the coaxial cable 6 to the ladder electrode 303. An earth shield 308 is mounted near the ladder electrode 303 so that the unnecessary plasma is not generated on the side opposite to the plane opposite to the substrate heater 2 of the ladder electrode 303.
The a-Si film is formed in the following procedure.
At first, the substrate 16 on which the a-Si thin film is formed is placed on the substrate heater 2 whose temperature is set, for example, to 200xc2x0 C. The SiH4 gas is introduced from the gas supply tube 17, for example, at the velocity of flow of 50 sccm. Then, the pressure within the reactor 1 is adjusted, for example, to 100 mTorr by adjusting the exhaust speed in the vacuum pump system (not shown) connected to the vacuum exhaust pipe 18.
The supply of the high frequency electric power causes the plasma to be generated between the substrate 16 and the ladder electrode 303. The impedance matching device 5 is adjusted such that the high frequency electric power is effectively fed to a region where a plasma 319 is generated. The SiH4 is decomposed in the plasma 319. The a-Si film is formed on the substrate 16. The a-Si film having the necessary thickness is formed, for example, by carrying out the film formation under the above-mentioned condition for about ten minutes.
The configuration examples shown in FIGS. 12 and 13 have the following two features, as compared with the configuration example of FIG. 11.
The first feature lies in the usage of the electrode referred to as the ladder type in which electrode bars of circular cross sections are assembled in the form of ladders without using the flat plate electrode as the electrode. This electrode has the feature that raw material can be uniformly supplied since the SiH4 gas of the raw material freely flows between the electrode bars.
The second feature lies in the fact that the power feeding operation is not carried out at only one point and it is carried out at a plurality of points (in this case, four points).
Presently, the low cost resulting from a film formation at the high speed and the high qualities such as a low defect density, a high crystallinity and the like are required of a thin film transistor for a flat panel display and a thin film semiconductor for a solar cell which are manufactured by using the above-mentioned technique and the like. As a new method of generating a plasma, which satisfies those requirements, there is a method of making a frequency of a high frequency power supply higher (30 MHz to 300 MHz). The fact that the higher qualities and the higher speed of the film formation are both attained by making the frequency higher is disclosed, for example, in xe2x80x9cDocument Mat. Res. Soc. Symp. Proc. Vol. 424, pp9, 1997xe2x80x9d. Especially, it has been recently known that this high frequency is suitable for a film formation at a high speed and at a high quality in a microcrystal Si thin film remarked as a new thin film instead of the a-Si.
By the way, the film formation through the high frequency operation has the defect that it is difficult to form a consistent wide area film. This reason is as follows. That is, a wavelength of a high frequency is at an order similar to a size of an electrode. Thus, a voltage distribution resulting from a standing wave mainly caused by a reflected wave occurring in an end of an electrode and the like is induced within the surface of the electrode, which makes the plasma nonuniform. This results in a nonuniform film formation.
In the configuration example exemplified as the {circle around (1)} usage of the parallel plate electrode, if the size of the electrode exceeds 30 cm or if the frequency exceeds 30 MHz, the influence of the standing wave becomes strong, which disables the attainment of a film formation uniformity of 10% that is at least necessary for the film formation of the semiconductor.
FIG. 14 is an example of a voltage distribution resulting from a standing wave at 100 MHz. FIG. 14 simultaneously shows an ion saturation current distribution. The ion saturation current distribution is substantially equal to an electron density distribution. Its measurement is easy. Thus, it is typically used as an index of a plasma distribution. From the voltage distribution, it is understood that the standing wave is induced on the electrode, which accordingly makes the ion saturation current distribution, namely, the plasma distribution nonuniform.
On the other hand, FIGS. 12, 13 exemplified as the {circle around (2)} usage of the ladder electrode have the feature that the standing wave largely induced in the case of the one-point power feeding operation can be reduced by using the four-point power feeding operation, in addition to the usage of the ladder electrode.
However, also in this case, if the size of the electrode exceeds 30 cm or the frequency exceeds 80 MHz, it is difficult to attain the uniform film formation.
FIG. 15 shows the voltage distributions generated on the ladder electrode when the four-point power feeding operation is done at 60 MHz and 100 MHz. Although it shows the relatively uniform voltage distribution at 60 MHz, it shows the nonuniform voltage distribution at 100 MHz.
Also, as for a four-point power feeding position, it is necessary to find out optimal positions in the manner of trial and error. Thus, this requires much labor and time.
Moreover, this has a problem that the change of the film formation conditions, such as the gas pressure and the high frequency electric power and the like, causes the optimal positions to be changed.
The above-mentioned problems are remarked in an academic society. Until now, a method of connecting a reactance (coil) without any loss to a side opposite to the power feeding side of the parallel plate has been proposed, for example, as noted in xe2x80x9cMat. Res. Soc. Symp. Proc. Vol. 377, pp33, 1995xe2x80x9d.
This reduces a voltage distribution generated on the electrode by changing the reflection condition from the electrode end of the standing wave and accordingly inducing on the electrode the portion where the distribution is relatively flat in the wave form of the standing wave, for example, the portion close to the peak of a sine wave. However, this method does not remove the standing wave at its source. It only generates on the electrode the flat portion in the sine wave. Thus, the portion where the uniform portion can be obtained is about xe2x85x9 of the wavelength. The uniformity about the range beyond it can not be attained in principle.
FIG. 16 shows a voltage distribution when an end of the parallel plate is terminated at a reactance (coil) without any loss at 100 MHz. In this way, a portion until about 30 cm from the end is uniform. However, a portion beyond it is nonuniform. Thus, this portion can not be used for the film formation.
The present invention is accomplished in view of the above mentioned circumstances. Therefore, an object of the present invention is to provide a discharge electrode for improving an uniformity at a discharge such as plasma, a high frequency plasma generator, a method of power feeding to a discharge electrode, and a method of manufacturing semiconductor device.
A numeral put in parentheses appearing the following description in which a device to solve the problem is represented correspondingly to a claim denotes that it corresponds to a member, a step or an operation in at least one embodiment in a plurality of embodiments in which a content noted in the claim is later-detailed. However, it is not intended that the solving device in the present invention is interpreted under the limitation on the member of the embodiment denoted by the numeral. It is intended to make the corresponding relation evident.
An electrical discharge electrode of the present invention is an electrical discharge electrode for producing a discharge (19) based on a fed high frequency electric power, including: an electrode body (3) to which the high frequency electric power is fed; and a reflected wave protect member (13) preventing an occurrence of a reflected wave of the high frequency electric power fed to the electrode body (3) in the electrode body (3). The discharge may be a plasma (19) generated by a discharging operation.
In the electrical discharge electrode of the present invention, the reflected wave protect member (13) further protects the reflected wave of the high frequency electric power from going into the electrode body (3).
In the electrical discharge electrode of the present invention, the reflected wave protect member (13) prevents an occurrence of a standing wave of the high frequency electric power in the electrode body (3).
In the electrical discharge electrode of the present invention, the electrode body (3) has an output section (9) outputting the fed high frequency electric power to an external portion of the electrode body (3), and wherein the reflected wave protect member (13) is connected to the output section (9) and is a load impedance to the high frequency electric power outputted from the output section (9).
In the electrical discharge electrode of the present invention, the load impedance substantially perfectly absorbs a traveling-wave component in the high frequency electric power outputted from the output section (9) to prevent the occurrence of the reflected wave in the electrode body (3).
In the electrical discharge electrode of the present invention, the load impedance has an impedance matching member (13) having a variable or fixed impedance and a resistor (14).
In the electrical discharge electrode of the present invention, the load impedance (413) has an impedance matching member (413) of which an impedance is variably adjusted, and wherein the impedance of the impedance matching member (413) is variably adjusted based on at least one of a high frequency electric power inputted to the load impedance (413), a high frequency electric power reflected from the load impedance (413), a high frequency electric power consumed in the load impedance (413), a high frequency electric power flowing through the load impedance (413), a voltage applied to the load impedance (413), a current flowing through the load impedance (413) and a phase difference between the current and the voltage of the load impedance (413).
In the electrical discharge electrode of the present invention, the impedance of the impedance matching member (413) is variably adjusted such that one of the high frequency electric power inputted to the load impedance (413) and the high frequency electric power consumed in the load impedance (413) becomes maximum or the high frequency electric power reflected from the load impedance (413) becomes minimum.
In the electrical discharge electrode of the present invention, the load impedance (913) has an impedance matching member (913) of which an impedance is variably adjusted, and wherein the impedance of the impedance matching member (913) is variably adjusted based on respective voltage values in a plurality of sections of the electrode body (3).
In the electrical discharge electrode of the present invention, the electrode body (3) is a ladder type electrode (303).
In the electrical discharge electrode of the present invention, the electrode body (3) receives the high frequency electric power from at least one or more power feeding point section (7) of the electrode body (3), and outputs the high frequency electric power from at least one or more end point section (9) of the electrode body (3), and wherein each of the power feeding point section (7) and the end point section (9) is arranged at a position symmetrical to each other in the electrode body (3).
In the electrical discharge electrode of the present invention, the electrode body (3) receives the high frequency electric power from at least one or more power feeding point section (7) of the electrode body (3), and outputs the high frequency electric power from at least one or more end point section (9) of the electrode body (3), and wherein each of the power feeding point section (7) and the end point section (9) is arranged such that current paths between all point sections in the electrode body (3) and the closest one of the power feeding point sections and the end point sections to one of the all point sections have distances equal to or shorter than xc2xc wavelength in a vacuum of the fed high frequency electric power.
In the electrical discharge electrode of the present invention, the electrode body (3) receives the high frequency electric power from at least one or more power feeding point section (7) of the electrode body (3), and outputs the high frequency electric power from at least one or more end point section (9) of the electrode body (3), and wherein a capacitance (1023) is connected in series between the reflected wave protect member (413) and the end point section (309) of the electrode body (3) or between the reflected wave protect member and a ground potential.
In the electrical discharge electrode of the present invention, the capacitance (1023) is a capacitance for bypassing the electrode body (3) in a manner of direct current.
A high frequency plasma generating apparatus of the present invention is a high frequency plasma generating apparatus having an electrical discharge electrode member (3) and generating a plasma based on a high frequency electric power fed to the electrical discharge electrode member (3), and wherein the electrical discharge electrode member (3) has a reflected wave protect member preventing an occurrence of a reflected wave of the high frequency electric power fed to the electrical discharge electrode member (3) in the electrical discharge electrode member (3).
A method of power feeding to an electrical discharge electrode of the present invention includes: providing an electrical discharge electrode (3) having an power feeding point section (7) and a non-specific point section (9) other than the power feeding point section (7); and feeding a high frequency electric power from the power feeding point section (7) to the electrical discharge electrode (3), and wherein the feeding the high frequency electric power includes feeding to the electrical discharge electrode (3) a traveling-wave component of a single-direction to the non-specific point section (9) from the power feeding point section (7), and not-feeding to the electrical discharge electrode (3) a reflected-wave component from the non-specific point section (9) to the power feeding point section (7).
A method of manufacturing a semiconductor by using a plasma CVD method of the present invention includes: providing a semiconductor substrate (16); providing an electrical discharge electrode (3) used in the plasma CVD method, which has a power feeding point section (7) and a non-specific point section (9) other than the power feeding point section; feeding a high frequency electric power from the power feeding point section (7) to the electrical discharge electrode (3); and generating a plasma (19) with the fed high frequency electric power to form a thin film on the semiconductor substrate (16) with the plasma (19), and wherein the feeding the high frequency electric power includes feeding to the electrical discharge electrode (3) a traveling-wave component of a single-direction to the non-specific point section (9) from the power feeding point section (7), and not-feeding to the electrical discharge electrode (3) a reflected-wave component from the non-specific point section (9) to the power feeding point section (7).
The invention of the high frequency discharge electrode of the present invention has at least one or more power feeding point and at least one or more end point. The supply of the high frequency electric power to the discharge electrode is carried out by one-way traveling-wave component from the one or more power feeding point to the one or more end point. An external circuit is connected to the end point so that a reflected wave component is not induced from the end point to the power feeding point.
A load impedance having a resistance component is used as the external circuit connected to the end point.
The load impedance is provided with a variable or fixed impedance matching device and a resistor.
It has an adjusting mechanism for measuring at least one of a high frequency electric power flowing into the load impedance, a high frequency electric power reflected from the load impedance, a high frequency electric power consumed in the load impedance, a voltage applied to the load impedance and a current flowing through the load impedance to adjust the matching device manually or automatically based on the measured value.
The matching device is automatically or manually adjusted such that the high frequency electric power flowing into the load impedance or the high frequency electric power consumed therein becomes maximum or the reflected power becomes minimum.
The high frequency voltage distribution on the electrode is measured to then adjust the matching device automatically or manually based on the distribution.
A ladder type electrode is used for the discharge electrode.
The power feeding point and the end point are arranged at the positions symmetrical to each other in the electrode.
The power feeding point and the end point are arranged such that the current path between any point on the electrode and the closest power feeding point or end point from the point has the distance equal to or shorter than a quarter of the vacuum wavelength of the power supply high frequency electric power.
A capacitor is connected in series between the load impedance and the end point of the high frequency electric power on the electrode or between an earth and the load impedance so that the electrode is bypassed in the manner of direct current.